Inhibitor material



Patented Apr. 22, 1930 UNITED STATES Examin PATENT OFFICE LUDWIG J. CHRISTMANN,

C'YANAMID COMPANY, 01

OF JERSEY CITY, NEW JERSEY, ASSIGNOB TO AMERICAN NEW YORK, N. Y., A CORPORATION OF MAINE INHIBITOR MATERIAL No. Drawing.

This invention relates to methods of cleaning or pickling metals by subjecting the same to an acid bath.

In the metal industries, particularly in the manufacture of iron or steel sheets or the like, which are to be coated with protective metals such as tin, zinc or cadmium, it is a common expedient to first clean the metal surface in order that the subsequent coating material may adhere firmly thereto, without danger of peeling off of the coating. This cleaning treatment usually consists in providing a dilute solution of a non-oxidizing mineral acid material, such as sulphuric acid, called a pickling bath, and immersing the metal articles to be cleaned in the bath for a length of time sutficient to remove scale, oxide and other matter from the surface of the metal. The bath is usually maintained at a predetermined temperature, usually above room temperature, during the pickling operation.

The acid in the pickling hath not only acts to remove the undesirable surface materials but also tends to attack the metal itself and, to protect the metal from attack by the acid, there is usually added to the pickling bath a small amount of a substance called an inhibitor. The inhibitor permits the acid to remove the undesirable surface material from the metal and prevents, either in whole or in part. the action of the acid upon the metal itself. Ordinarily, in the absence of an inhibitor, the acid in attacking the metal gives off a substantial quantity of hydrogen or other gaseous substances with the production of an acid mist or spray which is injurious to the workmen and, in addition, results in appreciable loss of acid.

The present invention is intended to provide an inhibitor which may be prepared easily, which is low in cost and which is highly effective in a pickling bath even though present in small amounts.

I have discovered that tetramethyldiam i ng diphentirlisulfide is highly etltive as an inhibitor in a pickling bath. This material may be obtained in any suitable and well known manner.

The inhibitor constituting the subject mat- Application filed September 18, 1929. Serial No. 893,590.

ter of my invention was tested in a pickling bath in the following manner:

A pickling solution was prepared consisting of 250 cc. of dilute sulphuric acid containing 6% by weight of 66 B. acid. The solution was placed in a suitable vessel, maintained at a temperature of 183185 F. and 0.100 grams of tetramethyl diamino diphenyl disulfide was added to the solution. This is equivalent to about 4 one-hundredths of one percent of inhibitor in the bath.

Strips 3% long and wide of 30 gauge tin plate stock were used for the tests. The specimens were first cleaned with ether to remove any oil or grease on the surface, and, after drying were immersed in the pickling bath for five minutes to remove the oxide scale. The specimens were removed from the bath, dried and weighed. The specimens were immediately returned to the pickling bath, immersed for twenty minutes, washed, dried and weighed again. The loss in weight was determined and the specimens were subjected to another 20 minute test. Throughout the tests, check runs were made with similar pickling baths but without using any inhibitor. The table given below shows the results obtained with and without tetramethyl diamino diphenyl disulfide in the pickling bath:

, Initial Imm. 20min 25 3,

weight loss in loss in ofstnp loss total mm 40min loss Grams Gram Grams NO inhibitor inbath.---. 4.147 100.0 Tetramethyl diamino diphenyl disulflde in bath 4.081 0.135 0.238 3.3 5.8

From the above it is clear that tetramethyl diamino diphenyl disulfide is a good inhibitor and effectively curtails the action of the acid upon the metal. This is particularly true in view of the fact that the sample pickled in the bath containing no inhibitor was so rapidly dissolved in the acid that before the end of forty minutes it was completely in solution. Therefore, no effort was made to weigh the check samples during the tests. In similar tests carried out at higher was and lower temperatures, it was found that the tetamethyl diamino diphenyl disulfide was equally effective as at temperatures originally described.

Although I have described my invention in some detail, it is not limited to the specific matters set forth. The amounts of inhibitor used in pickling baths may, of course, be varied wldely and the nature of the bath may also be changed to suit any particular conditions which may prevail. In general, it is not necessary to use more than 1% of inhibitor in the bath and for most purposes less than 0.1% is sufiicient. It is to be understood that my invention is not to be limited except as set forth in the claims appended hereto.

I claim:

1. A method of cleaning or pickling metals which comprises subjecting the same to a pickling or cleaning bath containing a small amount of tetramethyl diamino diphenyl disulfide.

2. A method of cleaning or pickling metals which comprises subjecting the same to a pickling bath containing less than 1% of tetramethyl diamino diphenyl disulfide.

3. A method of cleaning or pickling metals which comprises subjecting the same to a pickling or cleaning bath containing less than 0.1% of tetramethyl diamino diphenyl disulfide.

4. A method of cleaning or pickling metals which comprises subjecting the same to a pickling or cleaning bath containing about 0.01% of tetramethyl diamino diphenyl disulfide.

5. A bath for pickling metals comprising a non-oxidizing mineral acid and a small amount of tetramethyl diamino diphenyl disulfide.

6. A bath for pickling metals comprising a non-oxidizing mineral acid and less than 1% of tetramethyl diamino diphenyl disulfide.

7. A bath for pickling metals comprising a non-oxidizing mineral acid and less than 0.1% of tetramethyl diamino diphenyl disulfide.

8. A bath for pickling metals comprising sulphuric acid and about 0.01% of tetramethyl diamino di henyl disulfide.

In testimony wiereof, 'I have hereunto subscribed my name this 16th day of September, 1929.

LUDWIG J. CHRISTMANN. 

